Hydrocarbon dehydrogenation method and nonacidic multimetallic catalytic composite for use therein

ABSTRACT

Dehydrogenatable hydrocarbons are dehydrogenated by contacting them, at dehydrogenation conditions, with a catalytic composite comprising a combination of catalytically effective amounts of a platinum group component, a cobalt component, and a tantalum component with a porous carrier material. A specific example of the nonacidic catalytic composite disclosed herein is a combination of a platinum group component, a cobalt component, a tantalum component, and an alkali or alkaline earth component with a porous carrier material in amounts sufficient to result in a composite containing about 0.01 to about 2 wt. % platinum group metal, about 0.05 to about 5 wt. % cobalt, about 0.01 to about 5 wt. % tantalum, and about 0.1 to about 5 wt. % alkali metal or alkaline earth metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of my prior, copendingapplication Ser. No. 905,907 filed May 15, 1978 which issued as U.S.Pat. No. 4,199,438 on Apr. 22, 1980. All of the teachings of this priorapplication are specifically incorporated herein by reference.

The subject of the present invention is, broadly, an improved method fordehydrogenating a dehydrogenatable hydrocarbon to produce a hydrocarbonproduct containing the same number of carbon atoms but fewer hydrogenatoms. In another aspect, the present invention involves a methhod ofdehydrogenating normal paraffin hydrocarbons containing 3 to 30 carbonatoms per molecule to the corresponding normal mono-olefin with minimumproduction of side products. In yet another aspect, the presentinvention relates to a novel nonacidic multimetallic catalytic compositecomprising a combination of catalytically effective amounts of aplatinum group component, a cobalt component, a tantalum component, andan alkali or alkaline earth component with a porous carrier material.This nonacidic composite has highly beneficial characteristics ofactivity, selectivity, and stability when it is employed in thedehydrogenation of dehydrogenatable hydrocarbons such as aliphatichydrocarbons, naphthene hydrocarbons, and alkylaromatic hydrocarbons.

The conception of the present invention followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking function, and superior conversion,selectivity, and stability characteristics when employed in hydrocarbonconversion processes that have traditionally utilized dual-functioncatalytic composites. In my prior application Ser. No. 905,907, Idisclosed a significant finding with respect to a multimetalliccatalytic composite meeting these requirements. More specifically, Idetermined that a combination of cobalt and tantalum can be utilized,under certain specified conditions, to beneficially interact with theplatinum group component of a dual-function catalyst with a resultingmarked improvement in the performance of such a catalyst. Now I haveascertained that a catalytic composite, comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, and a tantalum component with a porous carrier material, canhave superior activity, selectivity and stability characteristics whenit is employed in a hydrocarbon dehydrogenation process if thesecomponents are uniformly dispersed in the porous carrier material in theamounts specified hereinafter and if the oxidation state of the metallicingredients are carefully controlled so that substantially all of theplatinum group component is present in the elemental metallic state,substantially all of the tantalum component is present in a positiveoxidation state, and substantially all of the catalytically availablecobalt component is present in the elemental metallic state or in astate which is reducible to the elemental metallic state underhydrocarbon dehydrogenation conditions or in a mixture of these states.I have discerned, moreover, that a particularly preferred multimetalliccatalytic composite of this type contains not only a platinum groupcomponent, a cobalt component, and a tantalum component, but also analkali or alkaline earth component in an amount sufficient to ensurethat the resulting catalyst is nonacidic.

The dehydrogenation of dehydrogenatable hydrocarbons is an importantcommercial process because of the great and expanding demand fordehydrogenated hydrocarbons for use in the manufacture of variouschemical products such as detergents, plastics, synthetic rubbers,pharmaceutical products, high octane gasoline, perfumes, drying oils,ion-exchange resins, and various other products well known to thoseskilled in the art. One example of this demand is in the manufacture ofhigh octane gasoline by using C₃ and C₄ mono-olefins to alkylateisobutane. Another example of this demand is in the area ofdehydrogenation of normal paraffin hydrocarbons to produce normalmono-olefins having 3 to 30 carbon atoms per molecule. These normalmono-olefins can, in turn, be utilized in the synthesis of a vast numberof other chemical products. For example, derivatives of normalmono-olefins have become of substantial importance to the detergentindustry where they are utilized to alkylate an aromatic, such asbenzene, with subsequent transformation of the product arylalkane into awide variety of biodegradable detergents such as the alkylaryl sulfonatetypes of detergents which are most widely used today for household,industrial, and commercial purposes. Still another large class ofdetergents produced from these normal mono-olefins are the oxyalkylatedphenol derivatives in which the alkylphenol base is prepared by thealkylation of phenol with these normal mono-olefins. Another class ofdetergents produced from these normal mono-olefins are the biodegradablealkylsulfonates formed by the direct sulfation of the normalmono-olefins. Likewise, the olefin can be subjected to directsulfonation with sodium bisulfite to make biodegradable alkylsulfonates.As a further example, these mono-olefins can be hydrated to producealcohols which then, in turn, can be used to produce plasticizers and/orsynthetic lube oils.

Regarding the use of products made by the dehydrogenation ofalkylaromatic hydrocarbons, they find wide application in the petroleum,petrochemical, pharmaceutical, detergent, plastic, and the likeindustries. For example, ethylbenzene is dehydrogenated to producestyrene which is utilized in the manufacture of polystyrene plastics,styrene-butadiene rubber, and the like products. Isopropylbenzene isdehydrogenated to form alpha-methylstyrene which, in turn, isextensively used in polymer formation and in the manufacture of dryingoils, ion-exchange resins, and the like materials.

Responsive to this demand for these dehydrogenation products, the arthas developed a number of alternative methods to produce them incommercial quantities. One method that is widely utilized involves theselective dehydrogenation of a dehydrogenatable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst at dehydrogenationconditions. As is the case with most catalytic procedures, the principalmeasure of effectiveness for this dehydrogenation method involves theability to perform its intended function with minimum interference ofside reactions for extended periods of time. The analytical terms usedin the art to broadly measure how well a particular catalyst performsits intended functions in a particular hydrocarbon conversion reactionare activity, selectivity, and stability, and for purposes of discussionhere, these terms are generally defined for a given reactant as follows:(1) activity is a measure of the catalyst's ability to convert thehydrocarbon reactant into products at a specified severity level whereseverity level means the specific reaction conditions used--that is, thetemperature, pressure, contact time, and presence of diluents such as H₂; (2) selectivity usually refers to the amount of desired product orproducts obtained relative to the amount of the reactant charged orconverted; (3) stability refers to the rate of change with time of theactivity and selectivity parameters--obviously the smaller rate implyingthe more stable catalyst. In a dehydrogenation process, morespecifically, activity commonly refers to the amount of conversion thattakes place for a given dehydrogenatable hydrocarbon at a specifiedseverity level and is typically measured on the basis of disappearanceof the dehydrogenatable hydrocarbon; selectivity is typically measuredby the amount, calculated on a mole or weight percent of converteddehydrogenatable hydrocarbon basis, of the desired dehydrogenatedhydrocarbon obtained at the particular activity or severity level; andstability is typically equated to the rate of change with time ofactivity as measured by disappearance of the dehydrogenatablehydrocarbon and of selectivity as measured by the amount of desireddehydrogenated hydrocarbon produced. Accordingly, the major problemfacing workers in the hydrocarbon dehydrogenation art is the developmentof a more active and selective catalytic composite that has goodstability characteristics.

I have now found a multimetallic catalytic composite which possessesimproved activity, selectivity, and stability when it is employed in aprocess for the dehydrogenation of dehydrogenatable hydrocarbons. Inparticular, I have determined that the use of a multimetallic catalyst,comprising a combination of catalytically effective amounts of aplatinum group component, a cobalt component, and a tantalum componentwith a porous refractory carrier material, can enable the performance ofa hydrocarbon dehydrogenation process to be substantially improved ifthe metallic components are uniformly dispersed throughout the carriermaterial in the amounts stated hereinafter and if their oxidation statesare carefully controlled to be in the states hereinafter specified.Moreover, particularly good results are obtained when this composite iscombined with an amount of an alkali or alkaline earth componentsufficient to ensure that the resulting catalyst is nonacidic andutilized to produce dehydrogenated hydrocarbons containing the samecarbon structure as the reactant hydrocarbon but fewer hydrogen atoms.This nonacidic composite is particularly useful in the dehydrogenationof long chain normal paraffins to produce the corresponding normalmono-olefin with minimization of side reactions such as skeletalisomerization, aromatization, cracking and polyolefin formation. In sum,the present invention involves the significant finding that acombination of a cobalt component and a tantalum component can beutilized under the circumstances specified herein to beneficiallyinteract with and promote a hydrocarbon dehydrogenation catalystcontaining a platinum group metal.

It is, accordingly, one object of the present invention to provide anovel method for the dehydrogenation of dehydrogenatable hydrocarbonsutilizing a multimetallic catalytic composite comprising catalyticallyeffective amounts of a platinum group component, a cobalt component, anda tantalum component combined with a porous carrier material. A secondobject is to provide a novel nonacidic catalytic composite havingsuperior performance characteristics when utilized in a dehydrogenationprocess. Another object is to provide an improved method for thedehydrogenation of normal paraffin hydrocarbons to produce normalmono-olefins which method minimizes undesirable side reactions such ascracking, skeletal isomerization, polyolefin formation,disproportionation and aromatization.

In brief summary, one embodiment of the present invention involves amethod for dehydrogenating a dehydrogenatable hydrocarbon whichcomprises contacting the hydrocarbon at hydrocarbon dehydrogenationconditions with a multimetallic catalytic composite comprising a porouscarrier material containing a uniform dispersion of catalyticallyeffective and available amounts of a platinum group component, a cobaltcomponent, and a tantalum component. Substantially all of the platinumgroup component is, moreover, present in the composite in the elementalmetallic state, substantially all of the tantalum component is presentin a positive oxidation state, and substantially all of thecatalytically available cobalt component is present in the correspondingelemental metallic state and/or in a state which is reducible to thecorresponding elemental metallic state under hydrocarbon dehydrogenationconditions. Further, these components are present in this composite inamounts, calculated on an elemental basis, sufficient to result in thecomposite containing about 0.01 to about 2 wt. % platinum group metal,about 0.05 to about 5 wt. % cobalt, about 0.01 to about 5 wt. %tantalum.

A second embodiment relates to the dehydrogenation method described inthe first embodiment wherein the dehydrogenatable hydrocarbon is analiphatic hydrocarbon containing 2 to 30 carbon atoms per molecule.

A third embodiment comprehends a nonacidic catalytic compositecomprising a porous carrier material having uniformly dispersed thereincatalytically effective and available amounts of a platinum groupcomponent, a cobalt component, a tantalum component, and an alkali oralkaline earth component. These components are preferably present inamounts sufficient to result in the catalytic composite containing, onan elemental basis, about 0.01 to about 2 wt. % platinum group metal,about 0.1 to about 5 wt. % of the alkali metal or alkaline earth metal,about 0.05 to about 5 wt. % cobalt, and about 0.01 to about 5 wt. %tantalum. In addition, substantially all of the platinum group componentis present in the elemental metallic state, substantially all of thetantalum component is present in a positive oxidation state,substantially all of the catalytically available cobalt component ispresent in the elemental metallic state and/or in a state which isreducible to the elemental metallic state under hydrocarbondehydrogenation conditions and substantially all of the alkali oralkaline earth component is present in a positive oxidation state.

Another embodiment pertains to a method for dehydrogenating adehydrogenatable hydrocarbon which comprises contacting the hydrocarbonwith the nonacidic catalytic composite described in the third embodimentat hydrocarbon dehydrogenation conditions.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimetalliccomposite preparation, suitable dehydrogenatable hydrocarbons, operatingconditions for use in the dehydrogenation process, and the likeparticulars. These are hereinafter given in the following detaileddiscussion of each of these facets of the present invention. It is to beunderstood that (1) the term "nonacidic" means that the catalystproduces less than 10% conversion of 1-butene to isobutylene when testedat dehydrogenation conditions and, preferably, less than 1% and (2) theexpression "uniformly dispersed throughout a carrier material" isintended to mean that the amount of the subject component, expressed ona weight percent basis, is approximately the same in any reasonablydivisible portion of the carrier material as it is in gross.

Regarding the dehydrogenatable hydrocarbon that is subjected to themethod of the present invention, it can, in general, be an organiccompound having 2 to 30 carbon atoms per molecule and containing atleast one pair of adjacent carbon atoms having hydrogen attachedthereto. That is, it is intended to include within the scope of thepresent invention, the dehydrogenation of any organic compound capableof being dehydrogenated to produce products containing the same numberof carbon atoms but fewer hydrogen atoms, and capable of being vaporizedat the dehydrogenation temperatures used herein. More particularly,suitable dehydrogenatable hydrocarbons are: aliphatic compoundscontaining 2 to 30 carbon atoms per molecule, alkylaromatic hydrocarbonswhere the alkyl group contains 2 to about 6 carbon atoms, and naphthenesor alkyl-substituted naphthenes. Specific examples of suitabledehydrogenatable hydrocarbons are: (1) alkanes such as ethanes, propane,n-butane, isobutane, n-pentane, isopentane, n-hexane, 2-methylpentane,3-methylpentane, 2,2-dimethylbutane, n-heptane, 2-methylhexane,2,2,3-trimethylbutane, and the like compounds; (2) naphthenes such ascyclopentane, cyclohexane, methylcyclopentane, ethylcyclopentane,n-propylcyclopentane, 1,3-dimethylcyclohexane, and the like compounds;and (3) alkylaromatics such as ethylbenzene, n-butylbenzene,1,3,5-triethylbenzene, isopropylbenzene, isobutylbenzene,ethylnaphthalene, and the like compounds.

In a preferred embodiment, the dehydrogenatable hydrocarbon is a normalparaffin hydrocarbon having about 3 to 30 carbon atoms per molecule. Forexample, normal paraffin hydrocarbons containing about 10 to 18 carbonatoms per molecule are dehydrogenated by the subject method to producethe corresponding normal monoolefin which can, in turn, be alkylatedwith benzene and sulfonated to make alkylbenzene sulfonate detergentshaving superior biodegradability. Likewise, n-alkanes having 10 to 18carbon atoms per molecule can be dehydrogenated to the correspondingnormal mono-olefin which, in turn, can be sulfonate or sulfated to makeexcellent detergents. Similarly, n-alkanes having 6 to 10 carbon atomscan be dehydrogenated to form the corresponding mono-olefin which can,in turn, be hydrated to produce valuable alcohols. Preferred feedstreams for the manufacture of detergent intermediates contain a mixtureof 4 or 5 adjacent normal paraffin homologues such as C₁₀ to C₁₃, C₁₁ toC₁₄, C₁₁ to C₁₅ and the like mixtures.

The multimetallic catalyst used in the present invention comprises aporous carrier material or support having combined therewith a uniformdispersion of catalytically effective amounts of a platinum groupcomponent, a cobalt component, a tantalum component, and, in thepreferred case, an alkali or alkaline earth component.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high-surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the dehydrogenation process, and it isintended to include within the scope of the present invention carriermaterials which have traditionally been utilized in dual-functionhydrocarbon conversion catalysts such as: (1) activated carbon, coke orcharcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated, for example, attapulgusclay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc.; (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, zinc oxide, magnesia, thoria, boria,silica-alumina; silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, MnAl₂ O₄, CaAl₂ O₄, and other like compounds having theformula MO.Al₂ O₃ where M is a metal having a valence of 2; and (7)combinations of elements from one or more of these groups. The preferredporous carrier materials for use in the present invention are refractoryinorganic oxides, with best results obtained with an alumina carriermaterial. Suitable alumina materials are the crystalline aluminas knownas gamma-, eta-, and theta-alumina, with gamma- or eta-alumina givingbest results. In addition, in some embodiments the alumina carriermaterial may contain minor proportions of other well-known refractoryinorganic oxides such as silica, zirconia, magnesia, etc.; however, thepreferred support is substantially pure gamma- or eta-alumina. Preferredcarrier materials have an apparent bulk density of about 0.2 to about0.8 g/cc and surface area characteristics such that the average porediameter is about 20 to about 300 Angstroms, the pore volume (B.E.T.) isabout 0.1 to about 1 cc/g and the surface area (B.E.T.) is about 100 toabout 500 m² /g. In general, best results are typically obtained with agamma-alumina carrier material which is used in the form of sphericalparticles having: a relatively small diameter (i.e. typically about 1/16inch), an apparent bulk density of about 0.2 to about 0.8 g/cc, a porevolume (B.E.T.) of about 0.3 to about 0.8 cc/g, and a surface area(B.E.T.) of about 100 to about 250 m² /g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or naturally occurring.Whatever type of alumina is employed, it may be activated prior to useby one or more treatments including drying, calcination, steaming, etc.,and it may be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide, to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, etc., and utilized in any desiredsize. For the purpose of the present invention, a particularly preferredform of alumina is the sphere; and alumina spheres may be continuouslymanufactured by the well-known oil drop method which comprises: formingan alumina hydrosol by any of the techniques taught in the art andpreferably by reacting aluminum metal with hydrochloric acid, combiningthe resultant hydrosol with a suitable gelling agent and dropping theresultant mixture into an oil bath maintained at elevated temperatures.The droplets of the mixture remain in the oil bath until they set andform hydrogel spheres. The spheres are then continuously withdrawn fromthe oil bath and typically subjected to specific aging treatments in oiland an ammoniacal solution to further improve their physicalcharacteristics. The resulting aged and gelled particles are then washedand dried at a relatively low temperature of about 300° F. to about 400°F. and subjected to a calcination procedure at a temperature of about850° F. to about 1300° F. for a period of about 1 to about 20 hours. Itis a good practice to subject the calcined particles to a hightemperature treatment with steam in order to remove undesired acidiccomponents such as residual chloride. This procedure effects conversionof the alumina hydrogel to the corresponding crystalline gamma-alumina.See the teachings of U.S. Pat. No. 2,620,314 for additional details.

Another particularly preferred alumina carrier material is synthesizedfrom a unique crystalline alumina powder which has been characterized inU.S. Pat. Nos. 3,852,190 and 4,012,313 as a by-product from a Zieglerhigher alcohol synthesis reaction as described in Ziegler's U.S. Pat.No. 2,892,858. For purposes of simplification, the name "Ziegleralumina" is used herein to identify this material. It is presentlyavailable from the Conoco Chemical Division of Continental Oil Companyunder the trademark Catapal. This material is an extremely high purityalpha-alumina monohydrate (boehmite) which after calcination at a hightemperature has been shown to yield a high purity gamma-alumina. It iscommercially available in three forms: (1) Catapal SB--a spray driedpowder having a typical surface area of 250 m² /g; (2) Catapal NG--arotary kiln dried alumina having a typical surface area of 180 m² /g;and (3) Dispal M--a finely divided dispersable product having a typicalsurface area of about 185 m² /g. For purposes of the present invention,the preferred starting material is the spray dried powder, Catapal SB.This alpha-alumina monohydrate powder may be formed into a suitablecatalyst material according to any of the techniques known to thoseskilled in the catalyst carrier material forming art. Spherical carriermaterial particles can be formed, for example, from this Ziegler aluminaby: (1) converting the alpha-alumina monohydrate powder into an aluminasol by reaction with a suitable peptizing acid and water and thereafterdropping a mixture of the resulting sol and a gelling agent into an oilbath to form spherical particles of an alumina gel which are easilyconverted to a gamma-alumina carrier material by known methods; (2)forming an extrudate from the powder by established methods andthereafter rolling the extrudate particles on a spinning disc untilspherical particles are formed which can then be dried and calcined toform the desired particles of spherical carrier material; and (3)wetting the powder with a suitable peptizing agent and thereafterrolling particles of the powder into spherical masses of the desiredsize in much the same way that children have been known to make parts ofsnowmen by rolling snowballs down hills covered with wet snow. Thisalumina powder can also be formed in any other desired shape or type ofcarrier material known to those skilled in the art such as rods, pills,pellets, tablets, granules, extrudates and the like forms by methodswell known to the practitioners of the catalyst carrier material formingart. The preferred type of carrier material for the present invention isa cylindrical extrudate having a diameter of about 1/32" to about 1/8"(especially about 1/16") and a length to diameter (L/D) ratio of about1:1 to about 5:1, with a L/D ratio of about 2:1 being especiallypreferred. The especially preferred extrudate form of the carriermaterial is preferably prepared by mixing the alumina powder with waterand a suitable peptizing agent such as nitric acid, acetic acid,aluminum nitrate and the like material until an extrudable dough isformed. The amount of water added to form the dough is typicallysufficient to give a loss on ignition (LOI) at 500° C. of about 45 to 65wt. %, with a value of about 55 wt. % being especially preferred. On theother hand, the acid addition rate is generally sufficient to provideabout 2 to 7 wt. % of the volatile free alumina powder used in the mix,with a value of about 3 to 4% being especially preferred. The resultingdough is then extruded through a suitably sized die to form extrudateparticles. It is to be noted that it is within the scope of the presentinvention to treat the resulting dough with an aqueous solution ofammonium hydroxide in accordance with the teachings of U.S. Pat. No.3,661,805. This treatment may be performed either before or afterextrusion, with the former being preferred. These particles are thendried at a temperature of about 500° F. to about 800° F. for a period ofabout 0.1 to about 5 hours and thereafter calcined at a temperature ofabout 900° F. to about 1500° F. for a period of about 0.5 to about 5hours to form the preferred extrudate particles of the Ziegler aluminacarrier material. In addition, in some embodiments of the presentinvention the Ziegler alumina carrier material may contain minorproportions of other well-known refractory inorganic oxides such assilica, titanium dioxide, zirconium dioxide, chromium oxide, berylliumoxide, vanadium oxide, cesium oxide, hafnium oxide, zinc oxide, ironoxide, cobalt oxide, magnesia, boria, thoria, and the like materialswhich can be blended into the extrudable dough prior to the extrusion ofsame. In the same manner crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with a multivalent cation, such as a rare earth, can beincorporated into this carrier material by blending finely dividedparticles of same into the extrudable dough prior to extrusion of same.A preferred carrier material of this type is substantially pure Ziegleralumina having an apparent bulk density (ABD) of about 0.3 to 1 g/cc(especially an ABD of about 0.4 to about 0.85 g/cc), a surface area ofabout 150 to about 280 m² /g (preferably about 185 to about 235 m² /g),and a pore volume of about 0.3 to about 0.8 cc/g.

The expression "catalytically available cobalt" as used herein isintended to mean the portion of the cobalt component that is availablefor use in accelerating the dehydrogenation reaction of interest. Forcertain types of carrier materials which can be used in the preparationof the instant catalyst composite, it has been observed that a portionof the cobalt incorporated therein is essentially bound-up in thecrystal structure thereof in a manner which essentially makes it more apart of the refractory carrier material than a catalytically activecomponent. Specific examples of this effect are observed when arefractory cobalt oxide or aluminate is formed by reaction of thecarrier material (or precursor thereof) with a portion of the cobaltcomponent and/or when the carrier material can form a spinel orspinel-like structure with a portion of the cobalt component. When thiseffect occurs, it is only with great difficulty that the portion of thecobalt bound-up with the support can be reduced to a catalyticallyactive state and the conditions required to do this are beyond theseverity levels normally associated with hydrocarbon dehydrogenationconditions and are in fact likely to seriously damage the necessaryporous characteristics of the support. In the cases where cobalt caninteract with the crystal structure of the support to render a portionthereof catalytically unavailable, the concept of the present inventionmerely requires that the amount of cobalt added to the subject catalystbe adjusted to satisfy the requirements of the support as well as thecatalytically available cobalt requirements of the present invention.Against this background then, the hereinafter stated specifications foroxidation state and dispersion of the cobalt component are to beinterpreted as directed to a description of the catalytically availablecobalt. On the other hand, the specifications for the amount of cobaltused are to be interpreted to include all of the cobalt contained in thecatalyst in any form.

One essential constituent of the acidic multimetallic catalyst of thepresent invention is a tantalum component. This component may in generalbe present in the instant catalytic composite in any catalyticallyavailable form in which the tantalum moiety is present in a positiveoxidation state such as a compound like the oxide, hydroxide, halide,oxyhalide, aluminate, or in chemical combination with one or more of theother ingredients of the catalyst. Although it is not intended torestrict the present invention by this explanation, it is believed thatbest results are obtained when the tantalum component is present in thecomposite in the form of tantalum oxide, tantalum aluminate, or tantalumoxyhalide or a mixture thereof, and the subsequently described oxidationand reduction steps that are preferably used in the preparation of theinstant catalytic composite are specifically designed to achieve thisend. The term "tantalum aluminate" as used herein refers to acoordinated complex of tantalum, oxygen, and aluminum which are notnecessarily present in the same relationship for all cases coveredherein. This tantalum component can be used in any amount which iscatalytically effective, with good results obtained, on an elementalbasis, with about 0.01 to about 5 wt. % tantalum in the catalyst. Bestresults are ordinarily achieved with about 0.05 to about 1 wt. %tantalum, calculated on an elemental basis.

This tantalum component may be incorporated in the catalytic compositein any suitable manner known to the art to result in a relativelyuniform dispersion of the tantalum moiety in the carrier material, suchas by coprecipitation or cogellation or coextrusion with the porouscarrier material, ion exchange with the gelled carrier material, orimpregnation of the carrier material either after, before, or during theperiod when it is dried and calcined. It is to be noted that it isintended to include within the scope of the present invention allconventional methods for incorporating and simultaneously uniformlydistributing a metallic component in a catalytic composite and theparticular method of incorporation used is not deemed to be an essentialfeature of the present invention. One preferred method of incorporatingthe tantalum component into the catalytic composite involves cogelling,coextrusion, or coprecipitating the tantalum component in the form ofthe corresponding halide or hydrous oxide during the preparation of thepreferred carrier material, alumina. This method typically involves theaddition of a suitable sol-soluble or sol-dispersable tantalum compoundsuch as finely divided tantalum pentachloride or tantalum pentoxidehydrate and the like to the alumina hydrosol and then combining thehydrosol with a suitable gelling agent and dropping the resultingmixture into an oil bath, etc., as explained in detail hereinbefore.Alternatively, the finely divided tantalum compound can be added to thegelling agent. After drying and calcining the resulting gelled carriermaterial in air, there is obtained an intimate combination of aluminaand tantalum oxide and/or oxyhalide and/or aluminate. Another method ofincorporating the tantalum component into the catalytic compositeinvolves utilization of a soluble, decomposable compound of tantalum toimpregnate the porous carrier material. In general, the solvent used inthis impregnation step is selected on the basis of the capability todissolve the desired tantalum compound without adversely affecting thecarrier material or the other ingredients of the catalyst--for example,a suitable alcohol, ether, acid and the like solvents. The solvent ispreferably an absolute alcohol or an aqueous, strongly acidic solution.Thus, the tantalum component may be added to the carrier material bycommingling the latter with a solution of suitable tantalum salt,complex, or compound such as tantalum pentabromide, tantalumpentachloride, tantalum pentafluoride, tantalum pentoxide hydrate (alsoknown as tantalic acid), tantalum oxytrichloride, the oxalic andtartaric complexes of tantalic acid, any of the soluble tantalate saltsuch as potassium fluorotantalate or potassium tantalate, and the likecompounds. A particularly preferred impregnation solution comprises anabsolute alcohol solution of tantalum pentachloride. In general, thetantalum component can be impregnated either prior to, simultaneouslywith, or after the other ingredients are added to the carrier material.However, excellent results are obtained when the tantalum component isadded to the carrier material prior to the platinum group and cobaltcomponents.

A second essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof as asecond component of the present composite. It is an essential feature ofthe present invention that substantially all of this platinum groupcomponent exists within the final catalytic composite in the elementalmetallic state. Generally, the amount of this component present in thefinal catalytic composite is small compared to the quantities of theother components combined therewith. In fact, the platinum groupcomponent generally will comprise about 0.01 to about 2 wt. % of thefinal catalytic composite, calculated on an elemental basis. Excellentresults are obtained when the catalyst contains about 0.05 to about 1wt. % of platinum, iridium, rhodium, or palladium metal. Particularlypreferred mixtures of these metals are platinum and iridium, andplatinum and rhodium.

This platinum group component may be incorporated in the catalyticcomposite in any suitable manner known to result in a relatively uniformdistribution of this component in the carrier material such ascoprecipitation or cogelation, ion exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium dioxide, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium chloroiridate, potassium rhodiumoxalate, etc. The utilization of a platinum, iridium, rhodium, orpalladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is ordinarilypreferred. Hydrogen chloride, nitric acid, or the like acid is alsogenerally added to the impregnation solution in order to furtherfacilitate the uniform distribution of the metallic componentsthroughout the carrier material. In addition, it is generally preferredto impregnate the carrier material after it has been calcined in orderto minimize the risk of washing away the valuable platinum or palladiumcompounds; however, in some cases it may be advantageous to impregnatethe carrier material when it is in a gelled state.

A third essential ingredient of the instant multimetallic catalyticcomposite is a cobalt component. Although this component may beinitially incorporated into the composite in many different decomposableforms which are hereinafter stated, my basic finding is that thecatalytically active state for hydrocarbon conversion with thiscomponent is the elemental metallic state. Consequently, it is a featureof this invention that substantially all of the catalytically availablecobalt component exists in the catalytic composite either in theelemental metallic state or in a state which is reducible to theelemental state under hydrocarbon dehydrogenation conditions or in amixture of these states. Examples of this last state are obtained whenthe catalytically available cobalt component is initially present in theform of cobalt oxide, hydroxide, halide, oxyhalide, and the likereducible compounds. As a corollary to this basic finding on the activestate of the catalytically available cobalt component, it follows thatthe presence of the catalytically available cobalt in forms which arenot reducible at hydrocarbon dehydrogenation conditions is to bescrupulously avoided if the full benefits of the present invention areto be realized. Illustrative of these undesired formes are cobaltsulfide and the cobalt oxysulfur compounds such as cobalt sulfate. Bestresults are obtained when the composite initially contains all of thecatalytically available cobalt component in the elemental metallic stateor in a reducible oxide state or in a mixture of these states. Allavailable evidence indicates that the preferred preparation procedurespecifically described in conjunction with the examples results in acatalyst having the catalytically available cobalt component present inthe form of a mixture of the reducible oxide and the elemental metal.Based on the performance of such a catalyst, it is believed thatsubstantially all of this reducible oxide form of the cobalt componentis reduced to the elemental metallic state when a dehydrogenationprocess using this catalyst is started-up and lined-out at hydrocarbondehydrogenation conditions. The cobalt component may be utilized in thecomposite in any amount which is catalytically effective, with thepreferred amount being about 0.05 to about 5 wt. % thereof, calculatedon an elemental cobalt basis. Typically, best results are obtained withabout 0.1 to about 2.5 wt. % cobalt. It is, additionally, preferred toselect the specific amount of cobalt from within this broad weight rangeas a function of the amount of the platinum group component, on anatomic basis, as is explained hereinafter.

The cobalt component may be incorporated into the catalytic composite inany suitable manner known to those skilled in the catalyst formulationart to result in a relatively uniform distribution of the catalyticallyavailable cobalt in the carrier material such as coprecipitation,cogelation, ion exchange, impregnation, etc. In addition, it may beadded at any stage of the preparation of the composite--either duringpreparation of the carrier material or thereafter--since the precisemethod of incorporation used is not deemed to be critical. However, bestresults are obtained when the catalytically available cobalt componentis relatively uniformly distributed throughout the carrier material in arelatively small particle or crystallite size having a maximum dimensionof less than 100 Angstroms, and the preferred procedures are the onesthat are known to result in a composite having a relatively uniformdistribution of the catalytically available cobalt moiety in arelatively small particle size. One acceptable procedure forincorporating this component into the composite involves cogelling orcoprecipitating the cobalt component during the preparation of thepreferred carrier material, alumina. This procedure usually comprehendsthe addition of a soluble, decomposable, and reducible compound ofcobalt such as cobalt acetate or chloride or nitrate to the aluminahydrosol before it is gelled. Alternatively, the reducible compound ofcobalt can be added to the gelling agent before it is added to thehydrosol. The resulting mixture is then finished by conventionalgelling, aging, drying, and calcination steps as explained hereinbefore.One preferred way of incorporating this component is an impregnationstep wherein the porous carrier material is impregnated with a suitablecobalt-containing solution either before, during, or after the carriermaterial is calcined or oxidized. The solvent used to form theimpregnation solution may be water, alcohol, ether, or any othersuitable organic or inorganic solvent provided the solvent does notadversely interact with any of the other ingredients of the composite orinterfere with the distribution and reduction of the cobalt component.Preferred impregnation solutions are aqueous solutions of water-soluble,decomposable, and reducible cobalt compounds such as cobaltous acetate,cobaltous benzoate, cobaltous bromate, cobaltous bromide, cobaltouschlorate and perchlorate, cobaltous chloride, cobaltic chloride,cobaltous fluoride, cobaltous iodide, cobaltous nitrate, hexamminecobalt(III) chloride, hexamminecobalt (III) nitrate, triethylenediamminecobalt(III) chloride, cobaltous hexamethylenetetramine, and the likecompounds. Best results are ordinarily obtained when the impregnationsolution is an aqueous solution of cobalt acetate or cobalt nitrate.This cobalt component can be added to the carrier material, either priorto, simultaneously with, or after the other metallic components arecombined therewith. Best results are usually achieved when thiscomponent is added simultaneously with the platinum group component viaan aqueous impregnation solution. In fact, excellent results areobtained with an impregnation procedure using a tantalum-containingcarrier material and an acidic aqueous impregnation solution comprisingchloroplatinic acid, cobalt acetate or nitrate and nitric acid.

A highly preferred ingredient of the catalyst used in the presentinvention is the alkali or alkaline earth component. More specifically,this component is selected from the group consisting of the compounds ofthe alkali metals--cesium, rubidium, potassium, sodium, and lithium--andof the alkaline earth metals--calcium, strontium, barium, and magnesium.This component exists within the catalytic composite in an oxidationstate above that of the elemental metal such as a relatively stablecompound such as the oxide or hydroxide, or in combination with one ormore of the other components of the composite, or in combination withthe carrier material such as, for example, in the form of an alkali oralkaline earth metal aluminate. Since, as is explained hereinafter, thecomposite containing the alkali or alkaline earth component is alwayscalcined or oxidized in an air atmosphere before use in thedehydrogenation of hydrocarbons, the most likely state this componentexists in during the use in the dehydrogenation reaction is thecorresponding metallic oxide such as lithium oxide, potassium oxide,sodium oxide, and the like. Regardless of what precise form in which itexists in the composite, the amount of this component utilized ispreferably selected to provide a nonacidic composite containing about0.1 to about 5 wt. % of the alkali metal or alkaline earth metal, and,more preferably, about 0.25 to about 3.5 wt. %. Best results areobtained when this component is a compound of lithium or potassium. Thefunction of this component is to neutralize any of the acidic materialsuch as halogen which may have been used in the preparation of thepresent catalyst so that the final catalyst is nonacidic.

This alkali or alkaline earth component may be combined with the porouscarrier material in any manner known to those skilled in the art toresult in a relatively uniform dispersion of this component throughoutthe carrier material with consequential neutralization of any acidicsites which may be present therein. Typically good results are obtainedwhen it is combined by impregnation, coprecipitation, ion-exchange, andthe like procedures. The preferred procedure, however, involvesimpregnation of the carrier material either before, during, or after itis calcined, or before, during, or after the other metallic ingredientsare added to the carrier material. Good results are ordinarily obtainedwhen this component is added to a tantalum-containing carrier materialsimultaneously with the platinum group and cobalt components in thepreferred impregnation procedure for these metallic components. It ispreferred to add the platinum group and cobalt components to thetantalum-containing carrier material, oxidize the resulting composite ina wet air stream at a high temperature (i.e. typically about 600° F. toabout 1000° F.), then treat the resulting oxidized composite with steamor a mixture of air and steam at a relatively high temperature of about800° F. to about 1050° F. in order to remove at least a portion of anyresidual acidity and thereafter add the alkali metal or alkaline earthcomponents. Typically, the impregnation of the carrier material withthis component is performed by contacting the carrier material with asolution of a suitable decomposable compound or salt of the desiredalkali or alkaline earth metal. Hence, suitable compounds include thealkali metal or alkaline earth metal halides, nitrates, acetates,carbonates, phosphates, and the like compounds. For example, excellentresults are obtained by impregnating the carrier material after theplatinum group cobalt and tantalum components have been combinedtherewith, with an aqueous solution of lithium nitrate or potassiumnitrate.

Regarding the preferred amounts of the metallic components of thesubject catalyst, I have found it to be a beneficial practice to specifythe amounts of these metallic components not only on an absolute basisbut also as a function of the amount of the platinum group component,expressed on an atomic basis. Quantitatively, the amount of the cobaltcomponent is preferably sufficient to provide an atomic ratio of cobaltto platinum group metal of about 0.1:1 to about 66:1, with the bestresults obtained at an atomic ratio of about 0.4:1 to about 18:1.Similarly, it is a good practice to specify the amount of the tantalumcomponent so that the atomic ratio of tantalum to platinum group metalcontained in the composite is about 0.1:1 to about 10:1, with thepreferred range being about 0.2:1 to about 5:1. In the same manner, theamount of the alkali or alkaline earth component is ordinarily selectedto produce a composite having an atomic ratio of alkali metal oralkaline earth metal to platinum group metal of about 5:1 to about 100:1or more, with the preferred range being about 10:1 to about 75:1.

Another significant parameter for the instant nonacidic catalyst is the"total metals content" which is defined to be the sum of the platinumgroup component, the cobalt component, the tantalum component, and thealkali or alkaline earth component, calculated on an elemental metalbasis. Good results are ordinarily obtained with the subject catalystwhen this parameter is fixed at a value of about 0.2 to about 5 wt. %,with best results ordinarily achieved at a metals loading of about 0.4to about 4 wt. %.

Integrating the above discussion of each of the essential and preferredcomponents of the catalytic composite used in the present invention, itis evident that an especially preferred nonacidic catalytic compositecomprises a combination of a platinum group component, a cobaltcomponent, a tantalum component, and an alkali or alkaline earthcomponent with an alumina carrier material in amounts sufficient toresult in the composite containing from about 0.05 to about 1 wt. %platinum group metal, about 0.1 to about 2.5 wt. % cobalt, about 0.25 toabout 3.5 wt. % alkali metal or alkaline earth metal, and about 0.05 toabout 1 wt. % tantalum. Regardless of the details of how the componentsof the catalyst are combined with the porous carrier material, theresulting multimetallic composite generally will be dried at atemperature of about 200° F. to about 600° F. for a period of from about1 to about 24 hours or more, and finally calcined or oxidized at atemperature of about 600° F. to about 1100° F. (preferably about 800° F.to about 1000° F.) in an air atmosphere for a period of about 0.5 to 10hours, preferably about 1 to about 5 hours, in order to convertsubstantially all of the metallic components to the corresponding oxideform. When acidic components are present in any of the reagents used toeffect incorporation of any one of the components of the subjectcomposite, it is a good practice to subject the resulting composite to ahigh temperature treatment with steam or with a mixture of steam andair, either before, during or after this oxidation step in order toremove as much as possible of the undesired acidic component. Forexample, when the platinum group component is incorporated byimpregnating the carrier material with chloroplatinic acid, it ispreferred to subject the resulting composite to a high temperaturetreatment with steam or a mixture of steam and air at a temperature ofabout 600° F. to about 1100° F. in order to remove as much as possibleof the undesired chloride.

The resultant oxidized catalytic composite is preferably subjected to asubstantially water-free reduction step prior to its use in thedehydrogenation of hydrocarbons. This step is designed to selectivelyreduce the platinum group component to the corresponding metal, whilemaintaining the tantalum component in a positive oxidation state and toinsure a uniform and finely divided dispersion of the metalliccomponents throughout the carrier material. It is a good practice to drythe oxidized catalyst prior to this reduction step by passing a streamof dry air or nitrogen through same at a temperature of about 500° F. toabout 1100° F. (preferably about 800° F. to about 950° F.) and at a GHSVof about 100 to 800 hr.⁻¹ until the effluent stream contains less than1000 ppm. of H₂ O and preferably less than 500 ppm. Preferably, asubstantially pure and dry hydrogen stream (i.e. less than 20 vol. ppm.H₂ O) is used as the reducing agent in this reduction step. The reducingagent is contacted with the oxidized catalyst at conditions including atemperature of about 600° F. to about 1200° F. (preferably about 800° F.to about 1100° F.), a GHSV of about 300 to 1000 hr.⁻¹, and a period oftime of about 0.5 to 10 hours effective to reduce substantially all ofthe platinum group component to the elemental metallic state, whilemaintaining the tantalum component in an oxidation state above that ofthe elemental metal. This reduction treatment may be performed in situas part of a start-up sequence if precautions are taken to predry theplant to a substantially water-free state and if a substantiallywater-free hydrogen stream is used.

Although using the subject catalyst in a substantially sulfur-free stateis an especially preferred mode of operation for the present hydrocarbondehydrogenation method (as explained in the teachings of my priorapplication Ser. No. 905,907), the resulting selectively reducedcatalytic composite may in some circumstances be beneficially subjectedto a presulfiding operation designed to incorporate in the catalyticcomposite from about 0.01 to about 0.5 wt. % sulfur, calculated on anelemental basis. Preferably, this presulfiding treatment takes place inthe presence of hydrogen and a suitable sulfur-containing sulfidingreagent such as hydrogen sulfide, lower molecular weight mercaptans,organic sulfides, etc. Typically, this procedure comprises treating theselectively reduced catalyst with a sulfiding reagent such as a mixtureof hydrogen and hydrogen sulfide having about 10 moles of hydrogen permole of hydrogen sulfide at conditions sufficient to effect the desiredincorporation of sulfur, generally including a temperature ranging fromabout 50° F. up to about 1100° F. or more. It is generally a goodpractice to perform this persulfiding step under substantiallywater-free conditions. Although not preferred, it is within the scope ofthe present invention to maintain or achieve the sulfided state of theinstant catalyst during use in the dehydrogenation of hydrocarbons bycontinuously or periodically adding a decomposable sulfur-containingcomound, such as the sulfiding reagents previously mentioned, to thereactor containing the catalyst in an amount sufficient to provide about1 to 500 wt. ppm. preferably 1 to 20 wt. ppm. of sulfur based onhydrocarbon charge.

According to the method of the present invention, the dehydrogenatablehydrocarbon is contacted with the multimetallic catalytic compositedescribed above in a dehydrogenation zone maintained at dehydrogenationconditions. This contacting may be accomplished by using the catalyst ina fixed bed system, a moving bed system, a fluidized bed system, or in abatch type operation; however, in view of the danger of attrition lossesof the valuable catalyst and of well-known operational advantages, it ispreferred to use a fixed bed system. In this system, the hydrocarbonfeed stream is preheated by any suitable heating means to the desiredreaction temperature and then passed into a dehydrogenation zonecontaining a fixed bed of the catalyst previously characterized. It is,of course, understood that the dehydrogenation zone may be one or moreseparate reactors with suitable heating means therebetween to ensurethat the desired conversion temperature is maintained at the entrance toeach reactor. It is also to be noted that the reactants may be contactedwith the catalyst bed in either upward, downward, or radial flow fashionwith the latter being preferred. In addition, it is to be noted that thereactants may be in the liquid phase, a mixed liquid-vapor phase, or avapor phase when they contact the catalyst, with best results obtainedin the vapor phase.

Although hydrogen is the preferred diluent for use in the subjectdehydrogenation method, in some cases other art-recognized diluents maybe advantageously utilized, either individually or in admixture withhydrogen or each other, such as steam, methane, ethane, carbon dioxide,and the like diluents. Hydrogen is preferred because it serves thedual-function of not only lowering the partial pressure of thedehydrogenatable hydrocarbon, but also of suppressing the formation ofhydrogen-deficient, carbonaceous deposits on the catalytic composite.Ordinarily, hydrogen is utilized in amounts sufficient to insure ahydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1, with bestresults obtained in the range of about 1.5:1 to about 10:1. The hydrogenstream charged to the dehydrogenation zone will typically be recycledhydrogen obtained from the effluent stream from this zone after asuitable hydrogen separation step. As is explained in my priorapplication Ser. No. 905,907, a highly preferred mode of operation ofthe instant dehydrogenation method is in a substantially water-freeenvironment; however, when utilizing hydrogen in the instant method,improved selectivity results are obtained under certain limitedcircumstances, if water or a water-producing substance (such as analcohol, ketone, ether, aldehyde, or the like oxygen-containingdecomposable organic compound) is added to the dehydrogenation zone inan amount calculated on the basis of equivalent water, corresponding toabout 1 to about 5,000 wt. ppm. of the hydrocarbon charge stock, withabout 1 to 1,000 wt. ppm. of water giving best results. This wateraddition feature may be used on a continuous or intermittent basis toregulate the activity and selectivity of the instant catalyst.

Regarding the conditions utilized in the method of the presentinvention, these are generally selected from the dehydrogenationconditions well known to those skilled in the art for the particulardehydrogenatable hydrocarbon which is charged to the process. Morespecifically, suitable conversion temperatures are selected from therange of about 700° F. to about 1200° F. with a value being selectedfrom the lower portion of this range for the more easily dehydrogenatedhydrocarbons such as the long chain normal paraffins and from the higherportion of this range for the more difficult to dehydrogenatehydrocarbons such as propane, butane, and the like hydrocarbons. Forexample, for the dehydrogenation of C₆ to C₃₀ normal paraffins, bestresults are ordinarily obtained at a temperature of about 800° F. toabout 950° F. The pressure utilized in ordinarily selected at a valuewhich is as low as possible consistent with the maintenance of catalyststability and is usually about 0.1 to about 10 atmospheres with bestresults ordinarily obtained in the range of about 0.5 to about 3atmospheres. In addition, a liquid hourly space velocity (calculated onthe basis of the volume amount, as a liquid, of hydrocarbon charged tothe dehydrogenation zone per hour divided by the volume of the catalystbed utilized) is selected from the range of about 1 to about 40 hr.⁻¹,with best results for the dehydrogenation of long chain normal paraffinstypically obtained at a relatively high space velocity of about 25 to 35hr.⁻¹.

Regardless of the details concerning the operation of thedehydrogenation step, an effluent stream will be withdrawn therefrom.This effluent will usually contain unconverted dehydrogenatablehydrocarbons, hydrogen, and products of the dehydrogenation reaction.This stream is typically cooled and passed to a hydrogen-separating zonewherein a hydrogen-rich vapor phase is separated from a hydrocarbon-richliquid phase. In general, it is usually desired to recover the unreacteddehydrogenatable hydrocarbon from this hydrocarbon-rich liquid phase inorder to make the dehydrogenation process economically attractive. Thisrecovery operation can be accomplished in any suitable manner known tothe art such as by passing the hydrocarbon-rich liquid phase through abed of suitable adsorbent material which has the capability toselectively retain the dehydrogenated hydrocarbons contained therein orby contacting same with a solvent having a high selectivity for thedehydrogenated hydrocarbon, or by a suitable fractionation scheme wherefeasible. In the case where the dehydrogenated hydrocarbon is amono-olefin, suitable adsorbents having this capability are activatedsilica gel, activated carbon, activated alumina, various types ofspecially prepared zeolitic crystalline aluminosilicates, molecularsieves, and the like adsorbents. In another typical case, thedehydrogenated hydrocarbons can be separated from the unconverteddehydrogenatable hydrocarbons by utilizing the inherent capability ofthe dehydrogenated hydrocarbons to easily enter into several well-knownchemical reactions such as alkylation, oligomerizaton, halogenation,sulfonation, hydration, oxidation, and the like reactions. Irrespectiveof how the dehydrogenated hydrocarbons are separated from the unreactedhydrocarbons, a stream containing the unreacted dehydrogenatablehydrocarbons will typically be recovered from this hydrocarbonseparation step and recycled to the dehydrogenation step. Likewise, thehydrogen phase present in the hydrogen-separating zone will be withdrawntherefrom, a portion of it vented from the system in order to remove thenet hydrogen make, and the remaining portion is typically recycledthrough suitable compressing means to the dehydrogenation step in orderto provide diluent hydrogen therefor.

In a preferred embodiment of the present invention wherein long chainnormal paraffin hydrocarbons are dehydrogenated to the correspondingnormal mono-olefins, a preferred mode of operation of this hydrocarbonrecovery step involves an alkylation reaction. In this mode, thehydrocarbon-rich liquid phase withdrawn from the hydrogen-separatingzone is combined with a stream containing an alkylatable aromatic andthe resulting mixture passed to an alkylation zone containing a suitablehighly acid catalyst such as an anhydrous solution of hydrogen fluoride.In the alkylation zone the mono-olefins react with alkylatable aromaticwhile the unconverted normal paraffins remain substantially unchanged.The effluent stream from the alkylation zone can then be easilyseparated, typically by means of a suitable fractionation system, toallow recovery of the unreacted normal paraffins. The resulting streamof unconverted normal paraffins is then usually recycled to thedehydrogenation step of the present invention.

The following working examples are introduced to illustrate further thedehydrogenation method and nonacidic multimetallic catalytic compositeof the present invention. These examples of specific embodiments of thepresent invention are intended to be illustrative rather thanrestrictive.

These examples are all performed in a laboratory scale dehydrogenationplant comprising a reactor, a hydrogen separating zone, heating means,cooling means, pumping means, compressing means, and the likeconventional equipment. In this plant, the feed stream containing thedehydrogenatable hydrocarbon is combined with a hydrogen-containingrecycle gas stream containing water in an amount corresponding to about100 wt. ppm. of the hydrocarbon feed and the resultant mixture heated tothe desired conversion temperature, which refers herein to thetemperature maintained at the inlet to the reactor. The heated mixtureis then passed into contact with the instant multimetallic catalystwhich is maintained as a fixed bed of catalyst particles in the reactor.The pressures reported herein are recorded at the outlet from thereactor. An effluent stream is withdrawn from the reactor, cooled, andpassed into the hydrogen-separating zone wherein a hydrogen-containinggas phase separates from a hydrocarbon-rich liquid phase containingdehydrogenated hydrocarbons, unconverted dehydrogenatable hydrocarbons,and a minor amount of side products of the dehydrogenation reaction. Aportion of the hydrogen-containing gas phase is recovered as excessrecycle gas with the remaining portion being continuously recycled,after water addition as needed, through suitable compressing means tothe heating zone as described above. The hydrocarbon-rich liquid phasefrom the separating zone is withdrawn therefrom and subjected toanalysis to determine conversion and selectivity for the desireddehydrogenated hydrocarbon as will be indicated in the examples.Conversion numbers of the dehydrogenatable hydrocarbon reported hereinare all calculated on the basis of disappearance of the dehydrogenatablehydrocarbon and are expressed in mole percent. Similarly, selectivitynumbers are reported on the basis of moles of desired hydrocarbonproduced per 100 moles of dehydrogenatable hydrocarbon converted.

All of the catalysts utilized in these examples are prepared accordingto the following preferred method with suitable modification instoichiometry to achieve the compositions reported in each example.First, a tantalum-containing alumina carrier material comprising 1/16inch spheres having an apparent bulk density of about 0.3 g/cc isprepared by: forming an aluminum hydroxyl chloride sol by dissolvingsubstantially pure aluminum pellets in a hydrochloric acid solution,admixing finely divided particles (i.e. 10 to 1000 microns in diameter)of tantalum pentachloride with hexamethylenetetramine, adding theresulting mixture of hexamethylenetetramine and tantalum pentachlorideto the alumina sol with sufficient agitation to uniformly disperse thetantalum pentachloride in the sol, gelling the resulting solution bydropping it into an oil bath to form spherical particles of atantalum-containing alumina hydrogel, aging, and washing the resultingparticles with an ammoniacal solution and finally drying, calcining, andsteaming the aged and washed particles to form spherical particles ofgamma-alumina containing substantially less than 0.1 wt. % combinedchloride and a uniform dispersion of tantalum in the form of tantalumoxide and/or aluminate. Additional details as to this method ofpreparing this alumina carrier material are given in the teachings ofU.S. Pat. No. 2,620,314.

The resulting tantalum-containing gamma-alumina particles are thencontacted in a first impregnation step at suitable impregnationconditions with a first aqueous impregnation solution containingchloroplatinic acid, cobalt nitrate or acetate and nitric acid inamounts sufficient to yield a final multimetallic catalytic compositecontaining a uniform dispersion of the hereinafter specified amounts ofplatinum and cobalt. The nitric acid is utilized in an amount of about 2wt. % of the alumina particles. In order to ensure a uniform dispersionof the metallic components in the carrier material, the impregnationsolution is maintained in contact with the carrier material particlesfor about 1/2 hour at a temperature of about 70° F. with constantagitation. The impregnated spheres are then dried at a temperature ofabout 225° F. for about an hour and thereafter calcined or oxidized inan air atmosphere containing about 5 to 25 vol. % H₂ O at a temperatureof about 600° F. to about 1100° F. (preferably about 800° F. to about1000° F.) for about 2 to 10 hours effective to convert all of themetallic components to the corresponding oxide forms. In general, it isa good practice to thereafter treat the resulting oxidized particleswith an air stream containing about 10 to about 30% steam at atemperature of about 800° F. to about 1000° F. for an additional periodof about 1 to about 5 hours in order to reduce any residual combinedchloride contained in the catalyst to a value of less than 0.5 wt. % andpreferably less than 0.2 wt. %.

In the cases shown in the examples where the catalyst utilized containsan alkali or alkaline earth component, this component is added to theoxidized and steam-treated multimetallic catalyst in a secondimpregnation step. This second impregnation step involves contacting theoxidized and steamed multimetallic catalyst with an aqueous acidicsolution of a suitable soluble and decomposable salt of the alkali oralkaline earth component under conditions selected to result in auniform dispersion of this component in the carrier material. For thecatalysts utilized in the present examples, the salts are lithiumnitrate or potassium nitrate. The amount of the alkali metal utilized ischosen to result in a final catalyst having the desired nonacidiccharacteristics. The resulting alkali or alkaline earth-impregnatedparticles are then preferably dried and oxidized in an air atmosphere inmuch the same manner as is described above following the firstimpregnation step. In some cases, it is possible to combine both ofthese impregnation steps into a single step, thereby significantlyreducing the time and complexity of the catalyst manufacturingprocedure.

The resulting oxidized catalyst is thereafter subjected to a drying stepwhich involves contacting the oxidized particles with a dry air streamat a temperature of about 930° F., a GHSV of 300 hr.⁻¹ for a period ofabout 10 hours. The dried catalyst is then purged with a dry nitrogenstream and thereafter selectively reduced by contacting with a dryhydrogen stream at conditions including a temperature of about 1050° F.,atmospheric pressure and a gas hourly space velocity of about 500 hr.⁻¹,for a period of about 1 to 10 hours effective to at least reducesubstantially all of the platinum group component to the correspondingelemental metal, while maintaining the alkali or alkaline earth andtantalum components is a positive oxidation state.

EXAMPLE I

The reactor is loaded with 100 cc of a catalyst containing, on anelemental basis, 0.3 wt. % platinum, 1.0 wt. % cobalt and 0.4 wt. %tantalum, and less than 0.15 wt. % chloride. This corresponds to anatomic ratio of tantalum to platinum of 1.4:1 and of cobalt to platinumof 11:1. The feed stream utilized is commercial grade isobutanecontaining 99.7 wt. % isobutane and 0.3 wt. % normal butane. The feedstream is contacted with the catalyst at a temperature of 1020° F., apressure of 10 psig., a liquid hourly space velocity of 4.0 hr.⁻¹, and arecycle gas to hydrocarbon mole ratio of 3:1. The dehydrogenation plantis lined-out at these conditions and a 20 hour test period commenced.The hydrocarbon product stream from the plant is continuously analyzedby GLC (gas liquid chromatography) and a high conversion of isobutane isobserved with a high selectivity for isobutylene.

EXAMPLE II

The catalyst contains, on an elemental basis, 0.375 wt. % platinum, 0.5wt. % cobalt, 0.35 wt. % tantalum, 0.6 wt. % lithium, and 0.15 wt. %combined chloride. These amounts correspond to the following atomicratios: (1) Ta/Pt of 1.0:1, (2) Co/Pt of 4.4:1, and (3) Li/Pt of 45:1.The feed stream is commercial grade normal dodecane. The dehydrogenationreactor is operated at a temperature of 850° F., a pressure of 10 psig.,a liquid hourly space velocity of 32 hr.⁻¹, and a recycle gas tohydrocarbon mole ratio of 5:1. After a line-out period, a 20 hour testperiod is performed during which the average conversion of the normaldodecane is maintained at a high level with a selectivity for normaldodecane of about 90%.

EXAMPLE III

The catalyst is the same as utilized in Example II. The feed stream isnormal tetradecane. The conditions utilized are a temperature of 830°F., a pressure of 20 psig., a liquid hourly space velocity of 32 hr.⁻¹,and a recycle gas to hydrocarbon mole ratio of 4:1. After a line-outperiod, a 20 hour test shows an average conversion of about 12%, and aselectivity for normal tetradecane of about 90%.

EXAMPLE IV

The catalyst contains, on an elemental basis, 0.3 wt. % platinum, 1.0wt. % cobalt, 0.4 wt. % tantalum, and 0.6 wt. % lithium, with combinedchloride being less than 0.2 wt. %. The pertinent atomic ratios are: (1)Ta/Pt of 1.4:1, (2) Co/Pt of 11:1, and (3) Li/Pt of 56:1. The feedstream is substantially pure cyclohexane. The conditions utilized are atemperature of 900° F., a pressure of 100 psig., a liquid hourly spacevelocity of 3.0 hr.⁻¹, and a recycle gas to hydrocarbon mole ratio of4:1. After a line-out period, a 20 hour test is performed with almostcomplete conversion of cyclohexane to benzene and hydrogen.

EXAMPLE V

The catalyst contains, on an elemental basis, 0.2 wt. % platinum, 0.5wt. % cobalt, 0.4 wt. % tantalum, 1.5 wt. % potassium, and less than 0.2wt. % combined chloride. The governing atomic ratios are: (1) Ta/Pt of2.2:1, (2) Co/Pt of 8.3:1 and (3) K/Pt of 37:1. The feed stream iscommercial grade ethylbenzene. The conditions utilized are a pressure of15 psig., a liquid hourly space velocity of 32 hr.⁻¹, a temperature of1010° F., and a recycle gas to hydrocarbon mole ratio of 3:1. During a20 hour test period, 85% or more of equilibrium conversion of theethylbenzene is observed. The selectivity for styrene is about 90%.

It is intended to cover by the following claims, all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formulation art or in the hydrocarbon dehydrogenation art.

I claim as my invention:
 1. A method for dehydrogenating a dehydrogenatable hydrocarbon comprising contacting the hydrocarbon, at hydrocarbon dehydrogenation conditions, with a catalytic composite comprising a porous carrier material containing, on an elemental basis, about 0.01 to about 2 wt. % platinum group metal, about 0.05 to about 5 wt. % cobalt, and about 0.01 to about 5 wt. % tantalum; wherein the platinum group, catalytically available cobalt and tantalum components are uniformly dispersed throughout the porous carrier material; wherein substantially all of the platium group component is present in the elemental metallic state; wherein substantially all of the tantalum component is present in a positive oxidation state; and wherein substantially all of the catalytically available cobalt component is present in the elemental metallic state or in a state which is reducible to the elemental metallic state under hydrocarbon dehydrogenation conditions or in a mixture of these states.
 2. A method as defined in claim 1 wherein the dehydrogenatable hydrocarbon is admixed with hydrogen when it contacts the catalytic composite.
 3. A method as defined in claim 1 wherein the platinum group component is platinum.
 4. A method as defined in claim 1 wherein the platinum group component is iridium.
 5. A method as defined in claim 1 wherein the platinum group component is rhodium.
 6. A method as defined in claim 1 wherein the platinum group component is palladium.
 7. A method as defined in claim 1 wherein the catalytic composite is in a sulfur-free state.
 8. A method as defined in claim 1 wherein the porous carrier material is a refractory inorganic oxide.
 9. A method as defined in claim 8 wherein the refractory inorganic oxide is alumina.
 10. A method as defined in claim 1 wherein the dehydrogenatable hydrocarbon is an aliphatic hydrocarbon containing 2 to 30 carbon atoms per molecule.
 11. A method as defined in claim 1 wherein the dehydrogenatable hydrocarbon is a normal paraffin hydrocarbon containing 3 to 30 carbon atoms per molecule.
 12. A method as defined in claim 1 wherein the dehydrogenatable hydrocarbon is naphthene.
 13. A method as defined in claim 1 wherein the dehydrogenatable hydrocarbon is an alkylaromatic, the alkyl group of which contains about 2 to 6 carbon atoms.
 14. A method as defined in claim 2 wherein the dehydrogenation conditions include a temperature of about 700° F. to about 1200° F., a pressure of about 0.1 to about 10 atmospheres, an LHSV of about 1 to about 40 hr.⁻¹, and a hydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1.
 15. A method as defined in claim 1 wherein the composite contains on an elemental basis, about 0.05 to about 1 wt. % platinum group metal, about 0.1 to about 2.5 wt. % cobalt and about 0.05 to about 1 wt. % tantalum.
 16. A method as defined in claim 1 wherein the metals content of the catalytic composite is adjusted so that the atomic ratio of tantalum to platinum group metal is about 0.1:1 to about 10:1 and the atomic ratio of cobalt to platinum group metal is about 0.1:1 to about 66:1.
 17. A method as defined in claim 2 wherein substantially all of the catalytically avaiable cobalt component contained in the composite is present in the elemental metallic state after the method is started-up and lined-out at hydrocarbon dehydrogenation conditions.
 18. A method as defined in claim 2 wherein the dehydrogenatable hydrocarbon is a normal paraffin hydrocarbon containing about 10 to about 18 carbon atoms per molecule.
 19. A method as defined in claim 2 wherein the dehydrogenatable hydrocarbon is an alkylaromatic, the alkyl group of which contains 2 to about 6 carbon atoms.
 20. A method as defined in claim 2 wherein the contacting is performed in the presence of water or a water-producing substance in an amount corresponding to about 1 to about 1000 wt. ppm. based on hydrocarbon charge. 